The invention relates to a pretreating agent used before painting a colorful coating steel plate, which consists of the following raw materials in weight portion: 1 to 40 portions of fluorozirconate, 1 to 40 portions of manganese phosphate, 1 to 40 portions of benzotriazole, and 20 to 60 portions of water. The pretreating agent has the following advantages: raw materials do not contain chromium, thus the pretreating agent has no effects on a human body and the environment; the pretreating agent can be suitable for use at normal temperature, thereby reflecting energy conservation; a steel plate is not needed to be sprayed with running water after the pretreating agent is used, thus the water resources can be saved; all the raw materials forming the pretreating agent can be easily obtained from the market and are only mixed evenly manually or mechanically to use, thus the pretreating agent is quite advantageous to be made and used by users in a production line so as to reflect the use convenience and save time; and the pretreating agent can be used for a long time, and is helpful to reflect the economical efficiency.